Transition metal catalyzed reactions have played a role in organic synthesis for a very long time. Twenty five years ago the first examples of the use of palladium as a catalyst for coupling reactions were disclosed. Since then enormous efforts have been devoted to extend the scope of palladium-catalyzed reactions. Among these, the Heck reaction.sup.1, the Stille reaction.sup.2 and the Suzuki reaction.sup.3 probably represent the most applied and most reliable reactions considering the reactions delivering new carbon-carbon bond formation. These reactions allow the presence of a wide variety of substituents attached to the reactants and merit special attention due to the simplicity of the experimental procedures. The Heck reaction, which is a vinylic substitution reaction, is most frequently conducted with olefines and organo halides or triflates as reactants. Couplings of organotin reagents with organo halides or triflates are named Stille reactions. The related couplings of organoboronic acids and/or organoboronic esters with organo halides or triflates are named Suzuki reactions. These reactions are of utmost importance in organic synthesis and have all found use in Combinatorial Chemistry (CC), sometimes as key reactions in the creation of chemical libraries.sup.4. Combinatorial Chemistry is conducted either in solution or preferably on solid phase. Combinatorial Chemistry combined with High Throughput Screening (HTS) has revolutionized the Drug Discovery Programmes in the pharmaceutical industry during the last few years.sup.5.
In Combinatorial Chemistry the reaction time factor is of importance. Rapid reactions are desired. The long reaction times often required in the palladium-catalyzed coupling reactions presented above is therefore in this respect a severe limitation. While some combinations of reactants allow fast conversions, and efficient use in Combinatorial Chemistry have been demonstrated, the majority of reactant combinations require unacceptable reaction times for completion. With regard to the palladium-catalyzed Heck, Stille or Suzuki reactions, attempted enhancement of the conversion rate by increasing the reaction temperature to over 130-150.degree. C. most often leads to collapse of the catalytic system before a full conversion is achieved. Product decomposition is frequently observed and a mixture of undesired side products are formed.